This study is a series of experimental investigation on the buckling strength of centrally and eccentrically loaded cold-formed square steel columns. In cold-formed square steel column sections, residual stress is introduced by cold-forming and welding, and at the same time, material strength is increased by the strain hardening and strain aging. These effetcs will strongly influence the buckling behavior of centrally and eccentrically loaded cold-formed square steel columns. This paper is to research local buckling behavior, and flexural buckling behavior of cold-formed square steel columns, and attempts to improve the predictability of performance of these products as structural compression members.